The proposed research is designed to analyze the processes underlying the changes in infant visual attention that occur as a function of experience with a stimulus. Preliminary studies show that at least two independent processes are involved: A memorial process controlling response decrements (habituation), and an arousal process controlling response increments (sensitization). In contrast to most previous work, which emphasized only the memorial process, the present project focuses on the sensitization process. One avenue of research will identify the stimulus determinants of the sensitization process. A technique called linear systems analysis is employed, which considers the "fit" between the physical properties of the stimulus and the characteristics of the infant's visual system (as estimated from contrast sensitivity). The most sensitizing stimuli may be those that closely match the infant's perceptual capabilities. Another line of research will investigate the contribution of sensitization to visual attention of different aged infants. A relatively high level of sensitization could have as much to do with the slow rate of response decrement observed with very young infants as does any memorial deficit. Finally, the interaction between sensitization and learning processes will be studied. Sensitization prolongs visual fixation and may, therefore, lead to better encoding of visual pattern stimuli. If two (or more) processes modulate infant visual attention, then the interpretation of infant visual fixation data must be reconsidered: Change in visual attention reflect not only cognitive factors, but also sensory and motivational factors. Researchers interested in the clinical use of visual fixation data must take into account the multiple determining factors involved.